Why stars twinkle — and where to see them shine brightest

Though light pollution has made the night sky harder than ever to observe, a clear and dark evening can reveal to the eye roughly 2,500 twinkling stars, according to The Atlantic. (There may be a septillion stars in the observable universe, but far fewer are visible to the naked human eye.)

There are few proofs as convincing as this — a sky crowded with flickering constellations — of the vastness of the universe. But even the stars’ signature twinkle signals something much greater.

The closest star in the sky, beyond our own, is Proxima Centauri, a cool 25 trillion miles away from the sun. One of the farthest visible, the Andromeda galaxy, is more than 14 quintillion miles away — that's a staggering 14 million trillions. Because it has traveled from such great a distance, the starlight that reaches Earth’s surface is little more than a spindly thread.

But that light does not waver. Starlight shines straight and true. (That is, barring some long-ago celestial event only visible to us now.) The twinkle we see is a result of these thin but steady strands of light hitting the Earth’s atmosphere and bouncing around: reflected by airborne particles here, scattered by gas molecules there. Because starlight’s path is so narrow — having traveled from so far away — it’s easy to see these minor deviations.

Planets, on the other hand, shine steadily in the night sky as seen from Earth’s surface. That’s because they are so much closer to us, and the light has a much shorter distance to travel. The light reflected off planets (whereas stars generate their own) has a much wider path than that of starlight.

When you look at a planet through a telescope, you see a solid sphere. When you look at stars through a telescope, all you see are pinpricks. (Their light has traveled too far for telescopes to make much difference.) And because the course of the light is broader, it’s harder to see how the light reflected off of planets is jostled around by Earth’s atmosphere.

From space, stars shine and planets reflect without interruption, meaning twinkling night stars are a phenomenon best experienced from Earth — preferably from an internationally-recognized dark sky reserve, where light pollution has yet to cloud those beautiful, glittering skies.

Stargazing hotspots and popular locations for astrophotography are mostly far-flung. Chile's Atacama Desert, for example, with its high altitudes and dry, non-polar air, has become a booming destination for astro-tourism. Of course, there are more accessible options, including Cherry Springs State Park in Pennsylvania and Mauna Kea in Hawaii (the 13,796-foot summit can be reached by car). But there are few places on Earth where you can better experience the magic of thousands of twinkling little stars piercing the night sky.